This invention relates to a composition consisting essentially of BiVO.sub.4, Al.sub.2 O.sub.3, and SiO.sub.2 which is useful as a yellow pigment, and a process for the preparation thereof.
A pigment is an insoluble small particle solid which is incorporated in paints, plastics, and inks to impart color and/or opacity. Ideally, a pigment should have strength, that is, a low color pigment requirement when mixed with a white pigment to make tints; intensity, that is, purity of shade and absence of dullness or grayness; lightfastness, that is, resistance to color change when exposed to sunlight in a pigmented article; and resistance to bleed, that is, low migration of color in a pigmented article. In addition for many applications it is desirable that a pigment have good hiding power, that is, ability to impart efficient opacifying power to a pigmented article.
The major intense yellow pigments currently used are lead chromate, cadmium sulfide, nickel titanate and a number of organic materials such as certain azo compounds. Lead chromate and cadmium sulfide have good hiding, however, presently there is a trend away from using these compounds because of their possible toxicity. Nickel titanate has good hiding power but it does not have the strength or high intensity desired in a high performance pigment. The organic pigments generally exhibit high strength, but poor hiding and frequently poor bleed resistance.
Thus there is a need for a nontoxic, high hiding, yellow pigment which also has good strength, high intensity, good lightfastness, and good resistance to bleed in organic solvents or vehicles.
Various references have described the synthetic preparation of bismuth vanadate, for example, I. M. Gottlieb and C. R. Rowe, "Preparation and Thermal Properties of Bismuth Orthovanadate", Thermal Analysis, Vol. 2, Proceedings Third ICTA DAVOS (1971), pp. 303-311; R. S. Roth and J. L. Waring, "Synthesis and Stability of Bismutotantalite, Stibiobantalite and Chemically Similar ABO.sub.4 Compounds", The American Mineralogist, Vol. 48 (Nov.-Dec. 1963) pp. 1348-56; H. E. Swanson et al., "Standard X-Ray Diffraction Powder Patterns", National Bureau of Standards Report, No. 7592 (Aug. 1962); Eduard Zintl and Ludwig Vanino, "Process For The Manufacture of Pure Bismuth Vanadate", German Pat. No. 422,947 (1925). However, none of the above were successful in preparing bismuth vanadate or a composition containing bismuth vanadate as a bright yellow pigment.